The law that states that mass cannot be created or destroyed in chemical or physical changes is the Law of Conservation of Mass.

This fundamental law of chemistry was first proposed by Antoine Lavoisier in the late 18th century. It states that in a closed system, the total mass of the reactants before a chemical reaction must equal the total mass of the products after the reaction. This means that mass is simply transformed from one form to another, but it is not lost or gained in the process.